1. Field of the Invention
The present invention relates to an imaging device and an imaging system including an analog-to-digital (AD) converter that converts a pixel signal output from a pixel into a digital signal. The invention also relates to a driving method of the imaging device.
2. Description of the Related Art
There is an imaging device including an AD converter that converts a pixel signal output from a pixel into a digital signal. An imaging device described in Japanese Patent Laid-Open No. 2007-281987 includes an AD converter corresponding to a pixel column. Also, in the imaging device described in Japanese Patent Laid-Open No. 2007-281987, a pixel outputs a noise signal and a photoelectric conversion signal, which is obtained by executing photoelectric conversion on incident light, to the AD converter. The AD converter of each column includes a first comparator that compares the noise signal with a first reference signal having a potential that is changed by a first changing quantity per unit time, and compares the photoelectric conversion signal with the first reference signal. Further, the AD converter of each column includes a second comparator that compares the noise signal with a second reference signal having a potential, which is changed by a larger second changing quantity per unit time than the first changing quantity, and that compares the photoelectric conversion signal with the second reference signal.